Of the total nitrate fertilizer used in the US, approximately 30% is lost due to over-application and subsequent seepage into groundwater, volatilization or tiling and runoff. Novel techniques in irrigation and soil moisture monitoring have provided growers the necessary data to manage irrigation, allowing for better forecasting and immediate feedback resulting in decreased water costs and optimized management practices.
However, a general lack of development in new technology for detailed management of soil nutrient levels has disallowed this same type of precision in fertilization. Currently, soil nutrients are monitored prior to and several times during the growing season by collecting 15-20 soil samples from across each 5-20 acre field and mailing these samples to off-site laboratories for analysis. Typically, nutrient testing is performed several times per growing season, resulting in addressable costs over $3 billion. Even with such a staggering cost figure, the investment does not always correlate to optimal crop yields. The lack of correlation is due to the inherent disconnect between the time the sample is taken and the results returned, during which time nitrate levels are affected by the action on ammonium of endogenous soil bacteria, seepage below the root zone with over-watering or over application of fertilizers, or degradation/volatilization during the drying process.
Efforts to improve the lag time between sample collection and actionable data have been made, but the process still typically requires between 3-5 business days, up to the best cases still requiring hours between sampling and results. All current direct methods of nitrate monitoring require pre-processing of the sample, and the nitrate is measured in the filtrate. This is due to the need for a good soil contact, which is typically lacking in standard ion-selective electrodes (ISEs).
Accordingly, a need remains for improved devices, systems, and methods for incorporation of a molecular receptor with a known affinity and selectivity for nitrate, providing a driving force for partitioning nitrate into the membrane, and allowing for direct measurement in soils of varying moisture. Additionally, there is a need for increased accuracy due to the selectivity of the receptor over typical non-specific ISE membranes. Embodiments of the invention address these and other limitations in the prior art.
The foregoing and other features of the invention will become more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.